Yogurt production process and products

ABSTRACT

Methods of preparation for cultured milk based products and products prepared thereby are provided wherein a yogurt base is produced having a viscosity of at least 75,000 cps. at time of manufacture and a total solids content of 27% to 31% by weight. The process involves rapid cooling to arrest fermentation under reduced backpressure by dispensing into a zone at atmospheric pressure followed by a shear step to modify viscosity to provide a high solids, high viscosity yogurt product. The high viscosity yogurt is particularly suitable for use as a component in parfait style yogurt products with at least one intermediate fruit layer. The high viscosity yogurt more effectively supports a fruit layer and facilitates fabrication of such parfait yogurt products. The yogurt base can further be characterized as increasing in viscosity by up to 25% from time of manufacture to time of consumption.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to food products and their methodsof preparation. More particularly, the present invention relates toimproved methods of preparation for cultured milk based products andproducts prepared thereby. More particularly, the improvement providesmethods of preparing high viscosity stirred style yogurt products.

BRIEF SUMMARY OF THE INVENTION

[0002] Yogurt is a nutritious popular dairy product. At retail, yogurtis now available in a wide assortment of varieties of texture, fatcontent, sweetener type and level, and flavor among other attributes.Other than aseptically packaged yogurt, yogurt is traditionallydistributed and consumed with a live culture that requires refrigerateddistribution (2° C. to 10° C.).

[0003] From a yogurt manufacturing process standpoint, all yogurts fallinto one of two styles; namely, 1) set yogurts, and 2) stirred style.The present invention finds particular suitability for use in connectionwith the provision of stirred style yogurts. Within these broad twoclassifications, numerous yogurt varieties exist.

[0004] In the set style, the manufacturer fills cups or containers withan inoculated but unfermented milk base and quiescently holds the filledcups at warm temperatures (≈40° C. to 50° C.) to allow the yogurt toferment therein. After the desired fermenting or maturing time, theproduct is cooled which arrests the culturing activity and also allowsthe body to set to form the gel-type texture. Set style yogurts have arelatively low initial viscosity (i.e., upon filling of its food packagecontainer) and a higher temperature (“temperature of filling”) comparedto the viscosity of stirred style yogurt products. As the productferments and then is cooled, its viscosity increases to its finalviscosity value. A set style yogurt is characterized by a more firm,gel-like consistency and a higher final viscosity than many stirredstyle yogurts. In addition to the natural thickening effect of theyogurt culture, a wide variety of thickeners and stabilizers are taughtas useful to supplement the yogurt's gel characteristics.

[0005] Of course, within this set style, there is a continuum of bodyfirmness. Most set custard style products have quite firm gels althoughsome others are much softer. One variety of a set style yogurt is a“custard” style yogurt. The softer gel products may even be perceived bythe consumer as being thinner than even certain stirred style products.

[0006] One popular style variant of custard style yogurt isfruit-on-the-bottom, also colloquially referred to as “sundae” style, inwhich a discrete layer of fruit preserves is on the bottom of the yogurtcontainer and the custard yogurt fills the rest of the container. Fruiton the top style products are similarly prepared, except that thecontainers are typically inverted after having been allowed to set.Typically, the yogurt phase is unflavored, although occasionallysweetened, and of a white or natural color. This white color is incontrast to the separate fruit preserve layer which often containsadditional coloring supplemental to that coloring provided by theingredients of the fruit preserves. An alternative, is to flavor and/orcolor the white mass to complement or contrast with the fruitpreparation. Other than for moisture equilibration, the yogurt layer andthe fruit preserve layer usually do not intermix over time due tospecific gravity difference and the binding effect of pectin in thefruit preserves.

[0007] In the second general category of yogurt products, the yogurt isof a stirred type. In producing stirred yogurt products, themanufacturer 1) ferments an inoculated milk base in bulk, e.g., in largestirred fermentation or culturing tanks, 2) cools the yogurt so formedto arrest the fermentation, and then 3) fills the individual yogurtcontainer with thickened yogurt. Such production facilities are run in acontinuous or semi-continuous manner. More specifically, afterfermentation to desired acidity and thickness, the yogurt is pumpedthrough cooling heat exchangers to arrest the fermentation. The coolingalso typically results in an increase in the viscosity of the yogurt.Flavorings and sweeteners can be admixed with the cooled yogurt and theyogurt is charged to containers. Conventionally, care needs to be takento minimize the shear imparted to the yogurt in practicing such processsteps to minimize the loss of thickness or viscosity built up by thefermentation step as augmented by cooling. Thus, the stirred styleyogurt typically has a higher viscosity than set style yogurts uponfilling due to the lower temperature and the thickening affect of yogurtculture. Nonetheless, the stirred style yogurt typically builds orincreases substantially in viscosity after filling over time untilreaching its intended finish viscosity. Of course, stirred yogurts alsocome in various styles and product variations.

[0008] Most commonly, fruit preserves or purees are stirred into thestirred yogurt immediately prior to filling. Such stirred style yogurtscomprising intermixed fruit purees are sometimes referred to mostfrequently as “Swiss” style or, less frequently but equivalently as“Continental” or “French” style. Occasionally, stirred Swiss styleyogurts are formulated with excessive amounts of stabilizers with theresult that after refrigerated storage for 48 hours, the yogurtpossesses a solid-like consistency, somewhat reminiscent of custardstyle yogurt.

[0009] A first “parfait” style yogurt can comprise two or more layers ofeach comprising differently colored and/or flavored stirred style yogurtlayers or portions. (See for example, U.S. Pat. No. 6,235,320 “ColoredMulti-layered Yogurt and Methods of Preparation” issued May 22, 2001 toDaravingas et al. and which is incorporated herein by reference.) Theyogurt layers or portions described therein are of high viscosity(15,000-30,000 cps) compared to conventional stirred yogurts (≈8,000 to12,000 cps.) to avoid intermixing of the parfait layers duringmanufacture, distribution and storage.

[0010] A second “parfait” or “trifles” style yogurt product can containa stirred style yogurt. The stirred “parfait” style yogurt product, canbe manufactured just prior to consumption, in which discrete layers offruit pieces are contained between layers of the stirred style yogurt.Typically, the yogurt phase is flavored, and of a white or naturalcolor. This white color is in contrast to the separate fruit pieceslayers which often are in a frozen state during production of the“parfait” yogurt product. The fruit pieces contained in the “parfait”are initially in a frozen state to minimize moisture equilibration andintermixing between the yogurt layer and the fruit pieces layer, thusextending product shelf-life providing a more organoleptically desirableproduct for the consumer. The stirred style “parfait” yogurt isgenerally characterized as having a viscosity of at least 40,000 cps.The yogurt thickness desirably assists in the separation of the yogurtand fruit piece layers of the “parfait” product.

[0011] As can be appreciated from the above description of the numerousstyles and flavors within styles of yogurts, product proliferation anddifferentiation is an important characteristic of commercial yogurtmanufacture. In this highly competitive food product category, there isa continuing desire to develop novel products having distinctive visual,taste, and textural variations in order to stimulate interest in yogurtsales.

[0012] The present invention finds particular suitability for use inconnection with the provision of stirred style yogurts. A gooddescription of preparing a fermented stirred yogurt is contained incommonly assigned U.S. Pat. No. 5,820,903 entitled “Calcium FortifiedYogurt and Methods of Preparation” (issued Oct. 13, 1998 to Fleury etal.) which is incorporated herein by reference.

[0013] The present invention resides in the addition of a processingstep after arresting fermentation. The improvement provides increasedthrough puts, surprisingly, the improvement additionally providesflexibility in altering the finished product viscosity, and theorganoleptic properties.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic process flow diagram illustrating the methodof preparation of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention relates to an improved method ofpreparation for cultured milk based products, more particularly yogurtproducts. The preparation steps as well as product components, productuse and attributes are described in detail below.

[0016] Referring now to the drawing, it can be seen that in the presentmethods generally designated by reference numeral 10, the firstessential step is to provide a warm fermented dairy base such as ayogurt. Conventional methods and techniques can be used to practice thisstep.

[0017] Conveniently, this first step can include the substeps of (1)providing a milk base 17, (2) homogenizing the milk base 19, (3)pasteurizing the homogenized milk base 21, (4) bringing the pasteurizedmilk base to fermenting temperatures 23 such as by cooling, (5) adding astarter culture 18, and (6) fermenting to desired acidities 27.

[0018] Briefly, the process typically begins with raw milk, that maycontain a combination of whole milk, skim milk, condensed milk, dry milk(dry milk solids non-fat or, equivalently, “MSNF”), grade A whey, creamand/or such other milk fraction ingredients as buttermilk, whey,lactose, lactalbumins, lactoglobulins, or whey modified by partial orcomplete removal of lactose and/or minerals, other dairy ingredients toincrease the nonfat solids content, which are blended to provide thedesired fat and solids content. While not preferred, the milk base caninclude a filled milk component, i.e., a milk ingredient having aportion supplied by a non-milk ingredient, e.g., oil or soybean milk.

[0019] While in the present invention, particular emphasis is directedtowards fermented bovine milk products such as yogurt, the skilledartisan will appreciate that the present invention is also suitable foruse in a wide variety of thickened dairy products, particularlyfermented dairy products such as kefir, sour cream and the like.

[0020] Also, while bovine milk is preferred, other milks can be used insubstitution for bovine milk whether in whole or in part, e.g., goat,sheep or equine milk.

[0021] The milk base 17 can further include sweeteners. The milk basecan optionally further comprise a nutritive carbohydrate sweeteningagent(s). Exemplary useful nutritive carbohydrate sweetening agentsinclude, but are not limited to, sucrose, high fructose corn syrup,dextrose, various DE (Dextrose Equivalent) corn syrups, beet or canesugar, invert sugar (in paste or syrup form), brown sugar, refiner'ssyrup, molasses (other than blackstrap), fructose, fructose syrup,maltose, maltose syrup, dried maltose syrup, malt extract, dried maltextract, malt syrup, dried malt syrup, honey, maple sugar, except tablesyrup and mixtures thereof.

[0022] Conveniently, the raw milk and sweeteners (such as fructose, cornsyrup, sucrose) can be blended in a first mix tank 11 and stored in amilk silo 13. Minor ingredients such as stabilizers and thickeners suchas starch, gelatin, pectin, agar carrageenan and mixtures thereof canalso be added if desired. The minor ingredients are combined with thesweetened milk to form the milk base 17 conveniently in a separatemixing vessel 15.

[0023] Next, the milk base 17 is homogenized 19 in a conventionalhomogenizer to disperse evenly the added materials and the fat componentsupplied by various ingredients thereby forming an homogenized milkbase. If desired, the milk base 17 can be warmed prior to homogenizationfrom typical milk storage temperatures of about 5° C. to temperatures ofabout 65° to 75° C.

[0024] This homogenized milk base is then pasteurized 21, typically byheating for times and temperatures effective to accomplishpasteurization to form a pasteurized milk base. As is well known, themilk base 17 can be heated to lower temperatures for extended time,e.g., 88° C. for 30 minutes, or alternately to higher temperatures,e.g., 95° C., for shorter times, e.g., for about 38 seconds. Of course,intermediate temperatures for intermediate times can also be employed.Other pasteurization techniques can be practiced (e.g., light pulse,ultra high pressure, etc.) if effective and economical. In certaincommercial practices, the sequence of the homogenization andpasteurization steps can be reversed.

[0025] The homogenized and pasteurized base is then brought toincubation temperature, usually about 40° to 46° C. When heatpasteurization is employed, this step typically is a cooling step 23.

[0026] Thereafter, the homogenized and pasteurized milk blend isinoculated with a desired culture 18. Usually, a combination ofLactobacillus bulgaricus and Streptococcus thermophilus bacteria isadded to begin the fermentation process. In other variations, the yogurtculture can additionally include a Lactbacillus bifidus and/or aLactbacillus acidophilus bacteria. The fermentation step 27, isquiescently continued until the pH of the milk blend reachesapproximately 4.4 to 4.6 endpoint to form a fermented dairy or yogurtbase. Depending upon temperature and amount of culture added, this maytake from about three to about 14 hours. It is important that themixture not be agitated during the fermentation process to allow propercurd formation. When the proper pH has been reached, the yogurt can bepumped through a shear valve.

[0027] The particular fermentation endpoint pH can vary modestly.Typically, the endpoint can range from about 4.2 to 4.6, preferablyabout 4.45 to 4.55.

[0028] The yogurt base thus prepared is characterized by a viscosity ofat least 15,000 cps. preferably at least 18,000 cps. (at 40° C. to 60°C.). Yogurt viscosities can range up to 20,000 cps. at this stage. Theyogurt base can further be characterized as having a total solidscontent of 27% to 33% by weight.

[0029] The present methods essentially comprise the step of thereaftercooling the yogurt 31 (e.g., to about 2° to 21° C.) to arrest furthergrowth and any further drop in the pH. In a preferred variation, thecooling step is performed rapidly, e.g., by passing through a heatexchanger having an average residence time of about 10 to 100 seconds.

[0030] Still referring to FIG. 1, it can be seen that the presentmethods also essentially comprise the step thereafter of discharging 32the cooled fermented dairy product into a zone maintained at atmosphericpressure. Conveniently, this step can be practiced by feeding ordischarging the yogurt base into a surge hopper 33 having a residencetime of 40 seconds or less, preferably 30 seconds or less, andthereafter the yogurt base is pumped through a valve 35, referred to asa shear valve. A bottom-fed surge hopper is preferred for theapplication. Although it can be appreciated that a variety of pumps aresuitable for pumping the yogurt base, preferred for use herein is aWaukesha Cherry-Burell Universal Series PD Pump Model 220-U2,manufactured by Waukesha Cherry Burell having an address of 611 SugarCreek Road, Delavan, Wis. 53115. The pump has a bi directional flow,large diameter shafts for greater strength, a rotor/shaft connectionsealed from the product zone, advanced sanitation capabilities includingclean-in-place, and can handle capacities of up to 310 gallons perminute (4914 l/s) with maximum pressure of up to 300 PSI (1950 KPa).

[0031] It will also be appreciated that a variety of shear valves may beemployed in this application, preferred for use herein is a Tri-Clovermodel 771 S-10M-14D-3-316L-FFY valve manufactured by Tri-Clover havingan address of P.O. Box 1413, Kenosha, Wis. 53141. The valve is preferredfor this application as a result of its capacity to maintain level andpressure controls of the product.

[0032] The implementation of the new step 32 in the production processhas surprisingly resulted in a two-fold through put increase forstandard yogurt products having a viscosity of at least 1,500 cps. Inone example, the through put at the arresting fermentation cooling stageincreased from 50 gallons per minute (755 l/s) to 100 gallons per minute(1585 l/s), without an increase in line pressures. Pressure through thepump and shear valve were maintained between 100 PSI (650 KPa.) to 150PSI (1000 KPa.), depending on the yogurt product formulation.

[0033] In another example, an ultra thick yogurt base having a viscosityof at least 40,000 cps. was cooled at a rate of 30 to 50 gallons perminute (475 l/s to 755 l/s) with a line pressure of 220 PSI (1430 KPa)using a standard yogurt production process wherein the surge hopper 33,pump and valve 35 are not contained in the system after the coolingstage 31. Surprisingly, the invention allows the same ultra thick yogurtproduct having a viscosity of at least 40,000 cps. to flow through thecooling stage at a rate of 60 gallons per minute (950 l/s) whilemaintaining a line pressure at 150 PSI (1000 KPa). The addition of thesurge hopper 33, and pump and shear valve 35 after the cooling stage 31eliminated a number of equipment issues associated with producing a highviscosity product. The high pressures associated with the typical yogurtproduction process caused pump failures, broken clamps, broken lines,etc. The new process eliminates or significantly reduces the equipmentissues, lengthening the life of the equipment, as well as reducing thefrequency of preventative maintenance check-ups required for theequipment.

[0034] The addition of the surge hopper, pump and shear valve after thecooling stage allows the fermented base to flow through the coolingplate at a lower back pressure than in the standard yogurt processwherein the fermented base is conveyed directly to the storage tank 37via a pump and shear valve 29 contained in the system prior to thecooling stage 31. In the present invention, the efficiency of thecooling stage 31 was not impaired despite higher flow rates. While notwishing to be bound by the proposed theory, it is theorized herein thatthe reduced back pressure allows standard stirred style yogurt and ultrathick stirred style yogurt to flow more freely through the coolingplates in the cooling stage utilizing an increased amount of theavailable cooling surface area.

[0035] The cold shearing of the yogurt base surprisingly improved thetextural properties of the finished product. By controlling the amountof shear, it is possible to texturize the finished product and producehigher viscosities than can be obtained from the standard yogurtprocess. For example, the finished yogurt product produced via thestandard yogurt process can be characterized as having a viscosity notgreater than 69,000 cps. Wherein, the same formula as above produced afinished yogurt product via the present invention that can becharacterized as having a viscosity greater than 70,000 cps., preferablygreater than 75,000 cps. at time of manufacture.

[0036] The yogurt base 37 thus prepared importantly is characterized bya viscosity of at least 55,000 cps., preferably at least 60,000 cps. Theresulting yogurt base can also be characterized as having a moredesirable organoleptic appeal, including having a more creamy mouthfeeland appearance.

[0037] In certain embodiments, particularly low fat and/or low calorievariations, the yogurt product herein comprises a high potencynon-nutritive carbohydrate sweetening agent. Exemplary high potencysweeteners include aspartame, sucrose, potassium acelsufame, saccharin,cyclamates, thaumatin and mixtures thereof. Especially preferred for useherein is aspartame.

[0038] If aspartame is employed, an aqueous dispersion 39 thereof can beprepared and added to the yogurt base. As illustrated in FIG. 1, anin-line static mixer 41 can be used to blend the slurry into the yogurtbase by static mixing to minimize shear. Minimum shear is desirable toavoid degrading the yogurt base's viscosity.

[0039] If desired, various flavors and colors 39 can be added with or ina manner similar to the aspartame dispersion. Illustrative flavorsinclude vanilla, chocolate, amaretto cheesecake, white chocolate, Bostoncream pie, caramel apple, banana cream pie, fruit flavors, and mixturesthereof.

[0040] If desired, the yogurt can additionally include a conventionalfruit sauce or puree. If present, the fruit constituent can compriseabout 5 to 15% of the yogurt product. The present method thus cancomprise the optional additional step of adding a fruit sauce or puree43. In the manufacture of Swiss-style yogurt, fruit flavoring is blendedsubstantially uniformly throughout the yogurt after fermentation iscomplete but prior to packaging 43. A second static mixer 51 can be usedto blend the fruit sauce into the yogurt with minimal shear.

[0041] In the manufacture of “sundae” style yogurt, fruit flavoring isdeposited at the bottom of the consumer container, and the container isthen filled with the yogurt mixture. To prepare a sundae style yogurtproduct employing a stirred style yogurt, the milk base is prepared withadded thickeners and/or stabilizers to provide upon resting a yogurttexture that mimics a “set” style yogurt. In this variation, the fruitis added directly to the container, typically to the bottom, prior tofilling with the yogurt.

[0042] The fruit flavoring sauce or puree used in the invention may beany of a variety of conventional fruit flavorings commonly used inyogurt products. Typical flavorings include strawberry, raspberry,blueberry, strawberry-banana, boysenberry, cherry-vanilla, peach,pineapple, lemon, orange and apple. Generally, fruit flavorings includefruit preserves and fruit or fruit puree, with any of a combination ofsweeteners, starch, stabilizer, natural and/or artificial flavors,colorings, preservatives, water and citric acid or other suitable acidto control the pH.

[0043] If desired, the milk base can be formulated with thickeners andsetting agents that will set up after cup filling that will impart atexture to the yogurt that mimics a set-style type yogurt product. Inthe present invention, a thickener can be used to produce a finishedyogurt product having a viscosity of 75,000 cps. to 100,000 cps. at timeof manufacture. The yogurt product thus produced can further becharacterized as having an increase in viscosity of up to 25% from thetime of manufacture to the time of consumption.

[0044] The products can additionally include a variety of otheringredients to increase their nutritional, organoleptic or otherconsumer appeal, e.g., fruit pieces, nuts, partially puffed cereals,etc.

[0045] The yogurt with or without fruit is then charged to aconventional container such as a coated paper or plastic cup. Afterfilling, the filled containers are applied with a lid or other closure,assembled into cases and entered into refrigerated storage fordistribution and sale. In one example, the yogurt is charged to a 32ounce container, shipped in a case in units of six, and then used tomanufacture a “parfait” fruit and yogurt layered product.

[0046] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. Method of producing a fermented dairy product, comprising the steps of: A. providing a warm fermented fluid dairy base at fermentation temperatures of 40° C. to 50° C. at a solids content of 27% to 31% by weight and a viscosity ranging from 15,000 cps. to 20,000 cps.; B. rapidly cooling the warm fermented fluid dairy base through a heat exchanger having an inlet pressure of 150 PSI (1000 KPa), to provide a cooled fermented dairy base whereby fermentation is arrested and the viscosity is increased; C. discharging the cooled fermented dairy base into a zone maintained at atmospheric pressure; and, D. thereafter, pumping the cooled fermented dairy base into a shear valve whereby the viscosity is further increased to provide a finished fermented dairy product having a viscosity of 75,000 cps. to 100,000 cps. at a temperature of 5° C.
 2. The method of claim 1 wherein the fermented dairy product is a yogurt having a viscosity of at least 75,000 cps. (at 5° C.).
 3. The method of claim 1 wherein the fermented dairy product is a yogurt having a viscosity of 75,000 cps. to 100,000 cps. (at 5° C.) at time of manufacture.
 4. The product produced by the method of claim 3 wherein the viscosity increases up to 25% from the time of manufacture to the time of consumer consumption.
 5. The product produced by the method of claim 3 having a total solids content of 27% to 31% by weight.
 6. The method of claim 1 wherein the fermented dairy product is a yogurt having a viscosity of 80,000 cps. to 90,000 cps. (at 5° C.) at time of manufacture.
 7. The product produced by the method of claim 6 wherein the viscosity increases up to 25% from the time of manufacture to the time of consumer consumption.
 8. The method of claim 1 wherein the fermented dairy product is a yogurt having a viscosity of 90,000 cps. to 100,000 cps. (at 5° C.) at time of manufacture.
 9. The product produced by the method of claim 8 wherein the viscosity increases up to 25% from the time of manufacture to the time of consumer consumption.
 10. The method of claim 1 wherein the zone of substep D is practiced employing a surge hopper exposed at atmospheric pressure.
 11. The method of claim 1 further comprising subsequently adding a flavor.
 12. The method of claim 1 further comprising subsequently adding a color.
 13. The method of claim 1 further comprising subsequently adding a non-nutritive carbohydrate sweetener.
 14. The method of claim 1 further comprising subsequently adding a fruit ingredient.
 15. The dairy product prepared in accordance with the process of claim
 1. 16. The yogurt product prepared in accordance with the process of claim
 2. 17. The yogurt product prepared in accordance with the process of claim
 3. 18. The yogurt product prepared in accordance with the process of claim
 4. 19. The yogurt product prepared in accordance with the process of claim
 5. 20. A yogurt product having a viscosity of 75,000 cps. to 100,000 cps. (at 5° C.) at time of manufacture.
 21. The product of claim 20 having a total solids content of 27% to 31% by weight.
 22. The product of claim 20 wherein the viscosity increases up to 25% from the time of manufacture to the time of consumer consumption.
 23. The product of claim 20 having a viscosity of 80,000 cps. to 90,000 cps. (at 5° C.) at time manufacture.
 24. The product of claim 20 having a viscosity of 90,000 cps. to 100,000 cps. (at 5° C.) at time of manufacture.
 25. The product of claim 20 further comprising subsequently adding a flavor.
 26. The product of claim 20 further comprising subsequently adding a color.
 27. The product of claim 20 further comprising subsequently adding a non-nutritive carbohydrate sweetener.
 28. The product of claim 20 further comprising subsequently adding a fruit ingredient. 